Adam I put up some detail on the PWM Dew heater thread last year on work I've done on sensing the dew point and on measuring the temp under heater straps. See the thread
http://www.iceinspace.com.au/forum/s...ead.php?t=8514 for that.
I'm in the midst of a rework of the controller and have obtained but not yet tested a cheaper temp/humidity sensor than the one I used originally.
I've not tried heating the primary with it so can't comment on that but for management of dew on the finderscope, eyepieces etc I've been very pleased with the results. I started an article on it some time ago but have not finished that yet. I hope to get to a point of having a design and part's list that relatively easily done on veroboard and not to hard to source the parts. I'm also having a try with a printed circuit board version but I'm still learning my way around that space.
Bob